As illustrated in FIGS. 1A and 1B, a piston pin 100 for connecting a piston 1 and a connecting rod 2 in an engine is formed in a cylindrical shape.
The piston pin 100 is fixed to the piston 1 through a snap ring 3 in a state where the piston pin 100 is passed through the upper end of the connecting rod 2 and the piston 1, thereby connecting the piston 1 and the connecting rod 2.
The conventional piston pin 100 is formed of a single material, and the piston pin 100 has the center of gravity which coincides with the geometric center of the piston pin 100.
Thus, since the piston pin 100 is not rotated when the engine operates, lubrication may not normally perform.
In order to solve such a problem, the piston pin 100 is manufactured to have an eccentric center of gravity with respect to the geometric center thereof. Then, the piston pin 100 is rotated when the piston 1 is lifted or lowered. When the piston pin 100 has an eccentric center of gravity, acceleration is applied in the vertical direction while the piston 1 is lifted or lowered. Then, the piston pin 100 is rotated to improve lubrication.
However, in order to manufacture the piston pin 100 with an eccentric center of gravity, bending deformation of the piston 1 or deformation in cross-sectional shape of the piston 1 must be considered. That is, in order to apply eccentricity in a state where the piston 1 is safely designed to prevent deformation of the piston pin 100, the inner diameter of the piston pin must be reduced while a minimum thickness is maintained. Thus, the weight of the piston pin 100 is increased. When the center of gravity of the piston pin 100 is eccentrically set without the increase in weight of the piston pin 100, a safety factor is inevitably damaged.